Staging: comedi: add ni_660x driver

Driver for National Instruments 660x counter/timer boards (PCI-6601,
PCI-6602, PXI-6602, and PXI-6608)

From: J.P. Mellor <jpmellor@rose-hulman.edu>
Cc: Herman Bruyninckx <Herman.Bruyninckx@mech.kuleuven.ac.be>
Cc: Wim Meeussen <Wim.Meeussen@mech.kuleuven.ac.be>
Cc: Klass Gadeyne <Klaas.Gadeyne@mech.kuleuven.ac.be>
Cc: David Schleef <ds@schleef.org>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>